I know Liverpool have worn yellow many times in the past, but their "traditional" away kit is white with red trim and black shorts, like the current away kit. It's a colour scheme that they had used for decades up until 1982, when the away kit was changed to the yellow kit that has been revived several times recently.
It could be argued that the yellow kit is "traditional" but I would say it certainly was a popular choice of colour that Liverpool used, and curiously enough many English club teams adopted yellow change kits during the 80's. However they first wore a yellow kit well before it became the official away kit..... strangely in 1966 at Anfield, when they had to wear an "emergency" yellow shirt in the second leg of a European Cup tie against Ajax. Back in those days the home team tended to change kit in the event of a colour clash in continental competition, and both the home and away kits clashed with Ajax's. The yellow kit was also used as a third kit in the 70's against teams who wore red and white, and in some FA Cup semi-finals.
Looking through the history of Liverpool's kits it does make sense to me that Adidas are going back in time with their choice of colours for the new away and third kits. The grey kit with red trim was first used in 1987 and used until 1991, during which time they won their last (to date) league championship, and the green kit was first used in 1991, and was a colour used in their away kits until the end of the previous Adidas sponsorship in 1996 (before Liverpool changed to Reebok). Since then they have worn écru (remember that one?
), amber and black, as well as white, yellow and green from before.
Lately it seems as if Adidas are making two away kits, one used in domestic competition, and the other for playing in Europe, which may also double up as a third kit. In which case, the green kit may get used in the Premier League when Liverpool play against teams in red and white, due to myopic officials (and you could argue the behest of television) regarding the grey kit as not being distinguishable enough from white.